This invention relates to the preparation of alkanol alkoxylates by the catalyzed addition reaction of alkylene oxides with alkanols. More specifically, this invention is directed to a process for the reaction of alkanols with alkylene oxides in the presence of a particular magnesium-containing co-catalyst system.
Alkanol alkoxylates (or simply alkoxylates, as the terminology is applied herein) are known materials having utility, for instance, as solvents, surfactants, and chemical intermediates. Alkoxylates in which the alkyl group has a number of carbon atoms in the detergent-range, i.e., from about 8 to 20, are common components of commercial cleaning formulations for use in industry and in the home.
Under conventional practice, alkoxylates are typically prepared by the addition reaction of alkylene oxides with alkanols. As an illustration, the preparation of an ethoxylate (represented by formula III below) by the addition of a number (n) of ethylene oxide molecules (formula II) to a single alkanol molecule (formula I) is represented by the equation ##STR1## where R is alkyl and n is an integer equal to or greater than one.
Alkoxylation reactions between alkylene oxides and alkanols are known to be necessarily carried out in the presence of a catalyst, which may be either of acidic or basic character. Recognized in the art as suitable basic catalysts are the soluble basic salts of the alkali metals of Group I of the Periodic Table, e.g., lithium, sodium, potassium, rubidium, and cesium, and the soluble basic salts of certain of the alkaline earth metals of Group II of the Periodic Table, e.g., barium, strontium, and calcium. With particular regard to magnesium-containing catalysts as are employed in the process of the present invention, the most relevant teachings of the art, specifically, those of U.S. Pat. Nos. 4,239,917, 4,210,764, and 4,223,164, indicate only that magnesium catalysts do not effectively promote the alkoxylation of detergent range alkanols under basic reaction conditions.
The use of a class of acidic catalysts for the alkoxylation reaction is also known, including, broadly, the Lewis acid or Friedel-Crafts catalysts. Specific examples of these catalysts are the fluorides, chlorides, and bromides of boron, antimony, tungsten, iron, nickel, zinc, tin, aluminum, titanium and molybdenum. The use of complexes of such halides with, for example, alcohols, ethers, carboxylic acids, and amines have also been reported. Still other examples of known acidic alkoxylation catalysts are sulfuric and phosphoric acids; the perchlorates of magnesium, calcium, manganese, nickel and zinc; metal oxalates, sulfates, phosphates, carboxylates and acetates; alkali metal fluoroborates; zinc titanate; and metal salts of benzene sulfonic acid. With specific regard to aspects or the process of the invention, while the art teaches alkoxylation catalyzed by a variety of acidic compounds of transition metals and metals of Groups III, IV, and V of the Period Table, it is not found to suggest a co-catalyst combination of acidic and basic compounds or the application of such acidic compounds as alkoxylation catalysts under basic reaction conditions.
Alkanolic solutions containing both basic magnesium compounds and compounds of certain transition metals are known (U.S. Pat. No. 4,178,300 to C.E.P.V. van der Berg), but have not been proposed to be useful in promoting ethoxylation reactions.
In preparation of the alkoxylates by the addition reaction between alkanols and alkylene oxides, there is obtained as product a mixture of various alkoxylate molecules having a variety of alkylene oxide adducts, e.g., different values for the adduct number n in formula III above. In certain preferred aspects, the present invention is a process characterized by enhanced selectivity for the preparation of alkoxylate mixtures in which a relatively large proportion of the alkoxylate molecules have a number (n) of alkylene oxide adducts that is within a relatively narrow range of values. It is known that alkoxylate products having such a narrow range distribution are preferred for use in detergent formulations. (Great Britian Pat. No. 1,462,134; Derwent Publications Research Disclosure number 194,010.) Narrow-range alkoxylates are also known to be particularly valuable as chemical intermediates in the synthesis of certain carboxyalkylated alkyl polyethers (U.S. Pat. No. 4,098,818) and of certain alkyl ether sulfates (Great Britain Pat. No. 1,553,561).
Conventional alkoxylation reactions promoted solely by the Lewis acid or Friedel-Crafts catalysts yield products having very desirable, narrow-range distributions of alkylene oxide adducts. However, the conventional use of acid catalysts is undesirable in several other processing aspects. For instance, the acids catalyze side reactions to produce relatively large amounts of polyalkylene glycols, and also react directly with components of the alkoxylation mixture to yield organic derivatives of the acids. Furthermore, efficient use of the acid catalysts is generally limited to the preparation of alkoxylates having an average number of ethylene oxide adducts, i.e., a value of n, that is no greater than about 2 or 3.
While conventional base-catalyzed alkoxylation reactions typically result in acceptably low levels of by-product formation and are not limited to the preparation of lower alkylene oxide adducts, they are known to produce only relatively broad-range alkoxylate products. It has recently been reported in the art (U.S. Pat. Nos. 4,210,764, 4,223,164, and 4,239,917, and the published European patent applications Ser. Nos. 0026544, 0026546 and 0026547) that ethoxylation promoted by basic barium, strontium, and calcium compounds compounds yields an alkoxylate product having a narrower distribution of alkylene oxide adducts than that of products of alkoxylation catalyzed by basic compounds of the alkali metals, particularly potassium and sodium. Still, the products of all such base-catalyzed alkoxylation reactions are of substantially broader distribution than that which would be desired or that which is obtained in the corresponding conventional acid-catalyzed reactions.